1. Field of the Invention
The present invention relates to a plasma display device suitable for use as a computer terminal display device or a destination display device.
2. Description of the Prior Art
In a plasma display device, a plurality of linear electrodes are arranged in parallel and closely spaced on each of a pair of insulating plates formed by a transparent, hard material such as, for example, glass, both insulating plates being opposed to each other so that the linear electrodes cross perpendicularly in the form of a matrix through a thin discharge space, the outer peripheral portion being sealed hermetically and the interior being evacuated and filled with an inert gas such as neon. An AC voltage is applied between selected ones of the linear electrodes to cause gas discharge between the intersecting points of the electrodes, thereby forming a predetermined luminous display pattern.
FIGS. 1(a) and (b) are sectional views showing a conventional plasma display device, in which the numeral 1 denotes a front glass as a display surface of a conventional plasma display device; numeral 2 represents a row of long, thin, strip-like front electrodes arranged on an inner surface of the front glass 1; numeral 6 denotes a rear glass disposed in opposed relation to the front glass 1 at a predetermined spacing; numeral 5 represents a row of long, thin, strip-like rear electrodes arranged on an inner surface of the rear glass 6 so as to form a matrix together with the front electrode row 2; numeral 7 denotes a sealing glass provided along the outer periphery of the front glass 1 and that of the rear glass 6 to seal the display portion formed by both electrode rows hermetically from the exterior; numeral 13 denotes a flexible printed circuit (hereinafter referred to as "FPC") soldered to each of the front electrode row 2 of the front glass 1 and that of the rear electrode row 5 to connect the display portion electrically to an external drive unit; and numeral 14 denotes a driving IC which receives an external display signal and causes corresponding display cells to emit light.
The arrangement of such a conventional plasma display device will now be described. The front glass 1 serves as the display surface of the display device, and supports the front electrode row 2 comprising image or character information displaying electrodes. The end portion of glass 1 has the electrodes of the front electrode row 2 drawn out to the exterior. The rear glass 6 supports the rear electrode row 5 spaced apart from the front electrode row 2 in the form of a matrix. The end portion of glass 6 has the electrodes of the rear electrode row drawn out to the exterior. The front and rear glass plates are sealed hermetically by the sealing glass 7. The thus-sealed space between both glass plates is filled with an inert gas such as neon. The electrode end portions of the front and rear glass plates 1, 6 are drawn out of the sealing glass 7 and exposed, then connected to the FPC 13 by soldering or the like for conduction with an external power source. Further, the driving IC 14 for selecting an intersecting point of matrix electrodes in the plasma display device, is mounted on the FPC 13. A high voltage is applied between the thus-selected front and rear electrodes, so that the encapsulated gas discharges to emit light and the corresponding points on the panel become luminous to effect a display pattern.
In the above construction of the conventional plasma display device, the surface of the electrode end portions which serve as connections and which are drawn out and exposed to the exterior for connection with the driving IC 14 are disposed in the direction opposite to the display surface, that is, in opposed relation thereto. Further, since the electrodes constitute a matrix, it is necessary that such electrode end portions be drawn out in two directions. This causes restrictions in the electrical connection of many terminals. Also in sealing both front and rear glass plates hermetically, serious problems are involved such as three-dimensional portions, e.g. corner portions, being present in the connection of both glass plates. Further, since the electrode end portions serving as connecting portions extend out from both the front and rear glass plates, the shape of the display portion (panel portion) is restricted.
The spacing between the hermetically-sealed front and rear glass plates is determined by the thickness of spacers (ribs) 15 each interposed between adjacent electrodes of the front electrode row 2 or the rear electrode row 5 as shown in FIG. 2. The ribs 15, which are generally black, are provided to prevent the emission of light by discharge of gas at an intersecting point between the matrix electrodes from spreading to the other portions. By the abutment of the ribs 15 with the front and rear glass plates 1, 6 there is determined the spacing between both glass plates. The thickness of spacers 15 is determined by the amount of luminance emitted by discharge, the kind of gas sealed, etc. Usually, such spacing is set at 100 .mu.m or so.
In order to obtain a rib thickness of about 100 .mu.m, the present inventors repeated printing on a glass plate using a black glass paste and a No. 200 mesh screen. The film thickness obtained by a single printing-drying-calcining cycle was about 20 .mu.m.+-.5 .mu.m. By repeating this cycle five times there could be obtained a thickness of about 100 .mu.m.
FIG. 3 is a normalized graph of a scattered thickness state of the resulting film at the end of each printing-drying-calcining cycle. As shown therein, the scatter in film thickness is about .+-.15 .mu.m at a resulting film thickness of about 100 .mu.m. This scatter is caused by various factors, including the mesh mark in printing, non-registration in overlap printing and variations in the viscosity of paste. Consequently, the spacing between both glass plates varies with scattering in the thickness of the ribs 15. Thus, the scatter in thickness varies device by device, and even in a single plasma display device, there occurs difference in rib thickness at some particular points, so that the said spacing is not uniform. Since the luminance amount of the light emitted depends on the spacing between both glass plates, the emitted light luminance distribution in the conventional display device is non-uniform.